Conventionally, elevators are provided with a safety gear which is triggered by an overspeed governor. In a common solution, when the elevator speed reaches a limit value preset in the overspeed governor, the overspeed governor triggers the safety gear by means of the same rope which transmits the elevator motion to the overspeed governor. The structure and operation of an overspeed governor of this type is described in U.S. Pat. No. 4,653,612.
In addition to overspeed situations, there are situations in which it should be possible to activate the safety gear of the elevator even if the elevator speed does not exceed the allowed limit. These situations include the testing of the safety gear in connection with the inspection of the elevator. For instance, certain elevators with a geared hoisting motor cannot normally be accelerated to the gripping speed, so checking the gripping function requires special measures. The usual solution for test operation in many overspeed governors is to provide the sheave with two rope grooves. The groove with the smaller diameter is intended for test situations. For a test, the driving rope is placed in this groove. Because of the change in the transmission ratio, this causes the overspeed governor to rotate faster than normally and the overspeed governor reaches the speed of rotation required for triggering the safety gear. A testing procedure like this takes plenty of working time. There are also possible fault situations in which it is necessary that the elevator can be stopped independently of the hoisting motor and working brake of the elevator. Such a fault situation is e.g. one in which the elevator starts moving from a floor with the doors completely or partially open.
At present, a further problem is that the overspeed governor has to be so placed that it can be accessed during inspection. If the elevator has a machine room, there is no problem, but in other solutions relating to the placement of the machinery, when the overspeed governor is placed in the elevator shaft, a separate inspection door is needed to allow the overspeed governor to be accessed in connection with an inspection.
The solutions proposed to solve the above-described problem include overspeed governor constructions in which a rotating part in the overspeed governor hits an obstacle brought into its path. The change in the postion or location of the rotating part resulting from the collision triggers the gripping function. For example, specifications DE B 1 236 153 and EP A 0 121 711 present solutions involving a collision between hard objects when an obstacle is brought into the path of a rotating part. The collision between the hard objects and the consequent requirement regarding a close mutual mounting tolerance between the colliding and rotating parts or alternatively a robust construction render overspeed governor constructions like those presented in the above-mentioned specifications expensive and/or problematic in operation.